Solid state storage devices (for example, solid state drives or SSDs) may be comprised of one or more packages of non-volatile memory dies implementing NAND memory cells, where each die is comprised of storage cells, where storage cells are organized into pages and pages are organized into blocks. Each storage cell can store one or more bits of information. Over time, a threshold voltage or resistance drift may occur in the memory cells where the resistance of the memory cells increases. As drift occurs, the read voltage used in the early life of the SSD is unable to read the data in the NAND memory cells. As resistance increases, a higher read voltage is applied to read data from the non-volatile memory cells. Other types of memory devices, such as phase change memory (PCM) cells, can experience drift, and may require a use of a higher read voltage if a memory cell has not been written within a predetermined time.
There is a need in the art for improved techniques for detecting drift in memory cells.